1. Field of the Invention
The present invention relates to a radiation detector of the type having a number of scintillators which emit light when radiation to be detected is incident thereon, the light being detected by photodiodes of a photodiode arrangement.
2. Description of the Prior Art
Radiation detectors of the above type are used in computed tomography systems, for example. If X-ray quanta are incident on the scintillators, which are composed of a suitable luminescent material, for example luminescent ceramic, the X-ray quanta are converted into light quanta. The light quanta are converted by the photodiodes into an electric current corresponding to the intensity of the light, and this current is amplified by an electronic unit and converted into digital data which are processed to form X-ray images by means of a computer associated with the computer tomography system.
In order to obtain a maximum light yield on the photodiode, the scintillators, composed of an optically transparent or translucent luminescent material, are surrounded by an optically reflective material on all sides except on their side facing the photodiode arrangement.
The scintillators are usually provided with a scattered radiation collimator whose collimator plates are oriented to the focus of an X-ray source interacting with the radiation detector, so that essentially only X-ray radiation emerging from the X-ray source can pass to the scintillators, while the scattered radiation produced when carrying out an examination in the object under examination is for the most part kept away from the scintillators.
In a known radiation detector of modular construction for a computed tomography system, each module has a photodiode arrangement with a number of photodiodes which are each assigned a scintillator. In this case, the scintillators are not separate elements since this would make it more difficult, if not impossible, to effect the exact positioning of the scintillators relative to the photodiodes.
A scintillator part is used whose length and width have a certain oversize relative to the length and width of the photodiode arrangement.
This scintillator part is encapsulated at its periphery and top side with a reflector coating, e.g. epoxy resin filled with titanium oxide, which serves as an optical reflector. In this case, a defined layer thickness is ensured at the periphery by special casting molds. At the top side, a defined layer thickness is ensured by mechanical processing in a special apparatus.
Afterward, the scintillator part is positioned on the photodiode arrangement by means of a special apparatus and adhesively bonded to said arrangement, in which case the apparatus can be removed again only after the adhesive bonding has cured.
The elements thus produced are laterally trimmed by special high-precision abrasive cutting machines and the scintillator element is slotted in such a way that each photodiode of the photodiode arrangement is allocated to a scintillator. In this case, particular attention must be paid to the slot depth in order to avoid damage to the photodiodes. So-called septa, for example aluminum foils coated on both sides, are adhesively bonded into the slots bounding the scintillators. The trimmed areas of the scintillator part are likewise bonded to septa.
Another manufacturing concept is based on adhesively bonding in each case a scintillator and a photodiode to one another and assembling a large number of such detector elements to form a radiation detector. It is possible in this case as well to combine a number of detector elements to form detector modules.
If it is intended to use a scattered radiation collimator, in both manufacturing concepts it is complicated and difficult to position the scattered radiation collimator before the adhesive bonding to the radiation detector or detector modules relative to the latter in the required manner. Therefore, complicated apparatuses are used in which the scattered radiation collimator and the radiation detector or the detector module must remain until the adhesive bonding has cured.